The Salvia miltiorrhiza (SM) has long been used in traditional Chinese medicine for treatment of cardiovascular and hepatic diseases. These plants have several components which can be extracted. Components of the root have been extracted initially with 95% ethanol followed by extraction with cold water or with hot water. Both fractions extracted in water have shown antiviral activity and have shown minimal toxicity in animals.
Retroviruses possess the ability to reverse the normal flow of genetic information from genomic DNA to mRNA. Although retroviruses are from a clearly defined and relatively homogeneous viral genus, they have been historically subdivided into three taxonomic groupings, primarily on the basis of the pathologic consequences of infection. The oncovirus subgroup includes retroviruses that have the ability to cause neoplastic disease in the infected host as well as several related, yet apparently benign viruses. Lentiviruses cause slow, chronic diseases that generally, although not always, lack a neoplastic component. Members of the spumavirus subgroup cause a marked foamy cytopathic effect in tissue culture. They have yet to be clearly associated with any human or animal disease.
Retroviral replication initiates with the intracytoplasmic penetration of the virion core, a process mediated by the specific interaction of the viral envelope glycoprotein with a specific cell surface receptor. Subsequently, a virion-associated RNA-dependent DNA polymerase transcribes the single-stranded RNA genome into a double-stranded linear DNA proviral intermediate (reverse transcription). Integration protein (integrase) specifically recognizes both ends of the viral DNA and removes two nucleotides from the 3'-ends (3'-donor processing). The processed viral DNA and integrase then migrate to the nucleus, where a viral integrase covalently links the retroviral genome to host chromosomal DNA (strand transfer), thereby forming the retroviral provirus.
The emergence of human immunodeficiency virus type (HIV) as an important human pathogen has led to a resurgence of scientific interest in retroviruses. In particular, scientific evidence indicates that the simple life cycle delineated above is not a completely accurate description of the replication cycle of all the members of this viral genus. For example, HIV-1 encodes no fewer than six gene products in addition to the characteristic retroviral Gag, Pol, and Env, and these are translated from a novel set of singly spliced and multiply spliced viral mRNA species. At least two of these additional proteins, termed Tat and Rev, act in trans to directly regulate HIV-1 gene expression. Therefore, the steps between penetration and proviral integration appeared quite similar for both MLV (murine leukemia virus) and HIV-1, although post-integration events were found to be significantly more complex in the latter. More recently, it has become evident that HIV-1 is merely one of a whole class of animal retroviruses that are now referred to as complex retroviruses. Retroviruses belonging to this complex retroviruses included all lentiviruses, spumaviruses, as well as HTLV-1 and related viruses (Table 1).
TABLE 1 __________________________________________________________________________ Major taxonomic divisions among retroviruses Category Subgroup Prototype Other examples __________________________________________________________________________ Simple retro- C-type retroviruses group A RSV ALV, ASV viruses C-type retroviruses group B MLV FeLV, MSV, SNV, REV, SSV B-type retroviruses MNTV D-type retroviruses MPMV SRV-1 Complex retro- Lentiviruses HIV-1 HIV-2, SIV, visna virus, FIV, viruses T-cell leukemia viruses Spuma- HTLV-1 EIAV HTLV-11, STLV, BLV viruses HSRV SFV, BFV __________________________________________________________________________ Abbreviationas: RSV, Rous sarcoma virus; ALV, avian leukemia virus; ASV, avian sarcoma virus; FeLV, feline leukemia virus; MSV, murine sarcoma virus; SNV, spleen necrosis virus; REV, reticuloendotheliosis virus; SSV, simian sarcoma virus; MMTV, mouse mammary tumor virus; MPMV, MasonPfizer monkey virus; SRV1, simian retrovirus type simian Tcell leukemia virus; BFV, bovine foamy virus
The importance of HIV-1 as a human pathogen has led to its being the major focus of research into lentivirus replication and gene regulation. Indeed, HIV-1 may be viewed as the prototype of not only the lentivirus subgroup but also, more broadly, complex retroviruses in general.
With respect to the development of anti-viral drugs, there are numerous attractive targets to inhibit the retrovirus life cycle (reverse transcriptase, protease, and integrase). To date, of the numerous compounds that have already been identified and approved for marketing by the FDA for HIV only reverse transcriptase and protease inhibitors have been identified.
Recent studies have demonstrated that combinatorial therapy against reverse transcriptase (RT) and protease can eliminate a majority of the HIV viruses in T lymphocytes. Unfortunately, the small fraction of remaining viruses mutate and continue to replicate even in the presence of these drugs. High rates of replication, viral sequence mutation, and rapid turnover of the viral population are typical traits of retroviruses. These traits are even more striking in the case of HIV-1.
Despite the significant progress that has been made in studying the molecular mechanisms of HIV, current anti-HIV chemotherapies have many shortcomings including toxic effects and the induction of resistant strains of virus after relatively short treatment periods. As result, these drugs lack needed long term benefits necessary for complete treatment or prevention of HIV-infection.
Currently used inhibitors of reverse transcriptase and protease, chemically complex molecules, are enormously expensive. Current estimates indicate that the typical HIV-1 positive patient will spend anywhere from $12,000-$20,000 per year. The 90% of people infected with HIV reside in the developing world, therefore, and even a majority of those in industrialized countries, could not possibly have access to these agents. Therefore, it is apparent that more economically feasible approaches must be sought.